The present invention relates to a perforating apparatus for forming a plurality of holes in the periphery of rod-shaped objects to be arranged at equal intervals and, more particularly, to a perforating apparatus which is suitable for forming a plurality of holes in the outer surface of filters of filter cigarettes.
Some conventional filter cigarettes have a plurality of holes formed in the outer periphery of their filters, these holes being formed at intervals in the circumferential direction of the filter. A smoker smoking this type of filter cigarette therefore inhales a large amount of air introduced into the filter through the holes, together with the cigarette smoke. With the cigarette smoke entering his mouth being diluted with air, the smoker is able to enjoy a lighter, milder taste. Moreover, because the smoke is diluted with air, its temperature is reduced, and thus the amount of harmful substances contained in the smoke is decreased.
A perforating apparatus as disclosed in U.S. Pat. No. 4,647,752 is a known apparatus for forming holes in filters of filter cigarettes. This perforating apparatus has a rotatable disc and a plurality of holding arms which are mounted on the periphery of the disc and spaced apart from one another in the circumferential direction thereof in order to hold individual filter cigarettes supplied thereto as the disc rotates. Therefore, as the disc rotates, the filter cigarettes are conveyed in the circumferential direction of the disc while being held by the holding arms. During conveyance of the filter cigarettes, each holding arm is rotated about the axis of the cigarette it is holding.
The perforating apparatus also has a generating source capable of radiating a laser beam in a pulse-like manner, and an optical system for guiding the laser beam emitted by the generating source to the outer periphery of a filter cigarette held by a holding arm. The optical system includes a single reflecting mirror for reflecting the laser beam and focusing lenses for focusing the laser beam reflected by the reflecting mirror on the outer periphery of the filter.
With the conventional perforating apparatus described above, the filter cigarettes held by the respective holding arms are rotated about their axes by rotation of the holding arms themselves while they are conveyed by rotation of the disc. In this state, when a laser beam is radiated on the outer periphery of the filter in a pulse-like manner, a plurality of holes are formed in the outer periphery of the filter to be arranged in the circumferential direction of the filter at intervals. Thereafter, a perforated filter cigarette is removed from the corresponding holding arm and conveyed to a packaging machine.
In the conventional perforating apparatus described above, a laser beam is sequentially focused on a filter of each filter cigarette while the filter cigarette is conveyed on a circular convey path. Therefore, the reflecting mirror of the optical system must be rotated about an axis of the disc so that each filter is irradiated with the laser beam. The reflecting mirror must be rotated at a large angular speed several times that of the disc so that holes are formed in the whole outer periphery of the filter in the circumferential direction by the laser beam. However, when a difference between the angular speeds of the disc, i.e., a filter cigarette and the reflecting mirror becomes large in this manner, the fall time of each pulse of the laser beam reflected by the reflecting mirror and radiated on the filter is prolonged. Therefore, it is difficult to form holes of a predetermined length on the outer periphery of each filter to be spaced apart from one another by a desired distance. More specifically, each hole formed in the outer periphery of the filter is undesirably elongated at its tail-side portion in the rotating direction of the filter, and an outer appearance of a filter cigarette as a final product is degraded.
The angular speeds of the disc and the reflecting mirror are increased in order to increase productivity of filter cigarettes per unit time, resulting in a large difference between these angular speeds. The larger the difference, the worse the outer appearance of the filter cigarette, and adjacent holes are connected to each other in a worst case.
In addition, when the angular speed of the reflecting mirror is increased, the load applied on the drive mechanism of the reflecting mirror is increased.